Since the cooling is very slow, we get coarse grained weak weld region. isnt?
The plates that are joined are huge structures. So are they subjected to any kind of local heat treatment (Induction heat treatment) ?
This depends primarily on how the material responds to heat treatment. Some materials will develop brittle phases in the heat-affected zone, such as high-carbon steels developing untempered martensite.
Conversely, most structural steels used in outdoor construction are intended to be welded without subsequent heat treatment.
If you are welding a heat-treatable steel, your options are to do a post-weld stress-relief or to heat above the martensite start temperature prior to welding.
Generally, heat treatment depends on the magnitude of carbon equivalent.
Carbon equivalent (CE) measures ability to form martensite, which is necessary for hydrogen cracking
CE < 0.35 no preheat or postweld heat treatment
0.35 < CE < 0.55 preheat
0.55 < CE preheat and postweld heat treatment
Generally, electroslag welding is a slow cooling welding process, here heat treatments is rarely used.
Electroslag welding produces large grain micro-structure because of the slow cooling rate. This microstructure has low toughness, so "normalizing" heat treatment is used to refine the grains and increses toughness.
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